The present invention relates generally to aircraft flight instrument systems and specifically to the airspeed indicator display portion and the altitude indicator display portion of a primary flight display.
Effective flight management is closely related to providing accurate and timely information to the pilot. The nature of the pilot's various tasks determines the general types of data which must be available. It is important to provide these data in a form best suited for use so that the pilot is not required to accomplish extensive mental processing before information can be used. If this occurs, then more information can be presented and utilized with less effort in mental processing. This can be expected to translate into fewer pilot errors. Computer generated displays offer significant advances in this direction.
Current electronic primary flight displays (PFD's) have a conventional attitude-director indicator (ADI) which consumes most of the available display area. The available display space for air data instruments is restricted to two strips on either side of the ADI. In the past, many display designers have settled upon the display format of the vertical tape presentation of airspeed and altitude.
Vertical tape air data displays have existed since before the advent of electronic display formats. There has been much debate about these displays and they have not been generally accepted as being equal in readability and ease of data interpretation to the round dial format. One factor that may have contributed to some acceptability of vertical tape displays could be their initial airframe application to large, stable, long range aircraft. These aircraft have to make few take off's and landings, and require virtually no significant enroute maneuvering. In this application, the data transfer from the tape displays has been satisfactory. However, application of tapes to smaller, dynamic airframes, with dynamic missions, has proven to not be as acceptable.
The general preference for the round dial format display apparently stems in part from our inherent societal training of reading round dials, e.g., clocks, speedometers, gas gauges and other dials where the markings or indices of the dial are fixed and a movable pointer or indicator moves relative to the fixed markings. However, the round or partially round dial format conveys information not only because of the position of the movable indicator relative to a fixed marking, but also because of the position of the indicator relative to the entire dial or simply the direction in which the movable indicator is pointing. This is illustrated by the existence of clock faces without numerals and in some instances clockfaces without any fixed markings. Notwithstanding the pilots societal background and experience with round style dials, pilots have learned how to satisfactorily use vertical tape displays. However, the experiences with dynamic airframes in the work load demand on the pilot to interpret the vertical tape data serves to still raise the general question of mental workload demand caused by vertical tape air data displays.
Also, information is conveyed by the round dial format due to direction and rate of movement or rotation of the movable indicator or pointer. Rate of movement is quite useful in the control of an aircraft. The round dial allows the pilot to judge the rate of movement towards a specific value e.g. airspeed target, or rate of movement through a range of values e.g. altitude changes during a climb and the pilot can evaluate these rate changes while simultaneously appreciating the macro situation with the relative position of the pointer on the dial.
With respect to clocks the usefulness of the terms clockwise and counterclockwise in communicating information is understood and well established. Further with respect to gauges and other round or partially round formats it is commonly understood that indicator movement in a clockwise direction or rotation indicates an increase and movement in a counterclockwise direction indicates a decrease.
Vertical tape formats, on the other hand, typically display information by moving the "dial", i.e., the scale or tape, and leaving the indicator, i.e. pointer, fixed. This approach is contrary to our previous societal experience and training and therefore does not represent good human factors engineering. However, the need for maximum data resolution in PFD's coupled with the reality of limited linear physical space has forced the display designer to this fixed pointer and moving tape combination.
A second approach to PFD's is to use a very large display area and to provide the altimeter and airspeed information in a round dial format. In addition to requiring a much larger display area, this approach results in a display that is no longer aligned in the traditional and widely accepted "basic T" format. The "basic T" flight instrument format is one in which the airspeed, attitude, altimeter and heading information form the shape of the letter "T" on the PFD.
Thus, a need exists for a PFD that provides the advantages of a round dial format for airspeed and altimeter information in the display space adjacent to a typical centrally located attitude director indicator while preserving the "basic T" instrument format.